that it is impossible for anyone to know anything. A weaker form would deny the actuality of our having knowledge, but leave open its possibility. Many skeptics have restricted their skepticism to a particular domain of supposed knowledge: e.g., knowledge of the external world, knowledge of other minds, knowledge of the past or the future, or knowledge of unperceived items. Such limited skepticism is more common than unrestricted skepticism in the history of epistemology. Arguments supporting skepticism come in many forms. One of the most difficult is the problem of the criterion, a version of which has been stated by the sixteenth-century skeptic Montaigne: ‘To adjudicate [between the true and the false] among the appearances of things, we need to have a distinguishing method; to validate this method, we need to have a justifying argument; but to validate this justifying argument, we need the very method at issue. And there we are, going round on the wheel.’ This line of skeptical argument originated in ancient Greece, with epistemology itself. It forces us to face this question: How can we specify what we know without having specified how we know, and how can we specify how we know without having specified what we know? Is there any reasonable way out of this threatening circle? This is one of the most difficult epistemological problems, and a cogent epistemology must offer a defensible solution to it. Contemporary epistemology still lacks a widely accepted reply to this urgent problem.
See also A PRIORI, COHERENTISM , FOUNDA- TIONALISM , JUSTIFICATION , PERCEPTION , SKEPTICISM , TRUT. P.K.M.